Pub Date : 1967-08-01DOI: 10.1088/0508-3443/18/8/312
L. E. Collins, P. Stroud
The statistical distribution of multiple emission of secondary electrons has been studied when He0 atoms in the energy range 1-5 kev impinge on pure aluminium in a secondary-electron scintillation detector. The results show that the distribution function is Poisson type, and by analysis of only two peaks on the pulse-height spectrum the fraction of incident He0 atoms which fail to cause the emission of an electron can be estimated. Secondary-electron coefficients γ have been obtained from the experimental distribution functions for He0 and Ar0 incident on Al. For He0, γ varied smoothly from 1·3 to 2·4 in the energy range 1-5 kev. The effect of argon ion-cleaning of the cathode has also been studied.
{"title":"The multiple emission of electrons in a secondary-electron particle counter","authors":"L. E. Collins, P. Stroud","doi":"10.1088/0508-3443/18/8/312","DOIUrl":"https://doi.org/10.1088/0508-3443/18/8/312","url":null,"abstract":"The statistical distribution of multiple emission of secondary electrons has been studied when He0 atoms in the energy range 1-5 kev impinge on pure aluminium in a secondary-electron scintillation detector. The results show that the distribution function is Poisson type, and by analysis of only two peaks on the pulse-height spectrum the fraction of incident He0 atoms which fail to cause the emission of an electron can be estimated. Secondary-electron coefficients γ have been obtained from the experimental distribution functions for He0 and Ar0 incident on Al. For He0, γ varied smoothly from 1·3 to 2·4 in the energy range 1-5 kev. The effect of argon ion-cleaning of the cathode has also been studied.","PeriodicalId":9350,"journal":{"name":"British Journal of Applied Physics","volume":"28 9 1","pages":"1121-1125"},"PeriodicalIF":0.0,"publicationDate":"1967-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82727263","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1967-08-01DOI: 10.1088/0508-3443/18/8/311
J. Dutton, W. T. Morris
Measurements of pre-breakdown ionization currents in uniform fields in dry air at pressures of about 1600 torr were carried out over a range of voltages from 165 kv to over 400 kv, corresponding to a range of values of the parameter p20d (p20 is the pressure reduced to 20°c and d is the electrode separation) from 500 to 12 600 torr cm. Over the whole range investigated the spatial growth of ionization was found to be in accordance with the well-known generalized Townsend equation. Moreover, at a value of p20ds of 12 200 torr cm (ds is the sparking distance), the sparking potential of 408 ± 9 kv predicted by using the Townsend breakdown criterion was in good agreement with the experimentally measured value of 4034 ± 05 kv. In these experiments the gas pressure and electrode separation were chosen so that the maximum value of the field used was less than about 60 kv cm-1. At this value field emission was negligible compared with the externally generated initial current I0 (similar 10-12 A), and values of I0 of this magnitude were shown, experimentally, not to give rise to significant space-charge effects in the measurement of pre-breakdown ionization. The values of the secondary ionization coefficient ω/ά were found to be markedly dependent on the state of the cathode surface showing that, just as at lower pressures and voltages, the cathode plays an important role in the breakdown process. At higher pressures (similar 5000 torr) and higher pre-breakdown fields (similar 100 kv cm-1) field emission currents of about 10-10 A were observed, which can be accounted for on the basis of the Fowler-Nordheim equation modified to take account of the presence of a thin insulating surface film: this work is currently being extended to the investigation of breakdown in these conditions, when space-charge distortion of the applied field due to high field emission from small cathode areas may become important.
{"title":"The mechanism of the electrical breakdown of air in uniform fields at voltages up to 400 kv","authors":"J. Dutton, W. T. Morris","doi":"10.1088/0508-3443/18/8/311","DOIUrl":"https://doi.org/10.1088/0508-3443/18/8/311","url":null,"abstract":"Measurements of pre-breakdown ionization currents in uniform fields in dry air at pressures of about 1600 torr were carried out over a range of voltages from 165 kv to over 400 kv, corresponding to a range of values of the parameter p20d (p20 is the pressure reduced to 20°c and d is the electrode separation) from 500 to 12 600 torr cm. Over the whole range investigated the spatial growth of ionization was found to be in accordance with the well-known generalized Townsend equation. Moreover, at a value of p20ds of 12 200 torr cm (ds is the sparking distance), the sparking potential of 408 ± 9 kv predicted by using the Townsend breakdown criterion was in good agreement with the experimentally measured value of 4034 ± 05 kv. In these experiments the gas pressure and electrode separation were chosen so that the maximum value of the field used was less than about 60 kv cm-1. At this value field emission was negligible compared with the externally generated initial current I0 (similar 10-12 A), and values of I0 of this magnitude were shown, experimentally, not to give rise to significant space-charge effects in the measurement of pre-breakdown ionization. The values of the secondary ionization coefficient ω/ά were found to be markedly dependent on the state of the cathode surface showing that, just as at lower pressures and voltages, the cathode plays an important role in the breakdown process. At higher pressures (similar 5000 torr) and higher pre-breakdown fields (similar 100 kv cm-1) field emission currents of about 10-10 A were observed, which can be accounted for on the basis of the Fowler-Nordheim equation modified to take account of the presence of a thin insulating surface film: this work is currently being extended to the investigation of breakdown in these conditions, when space-charge distortion of the applied field due to high field emission from small cathode areas may become important.","PeriodicalId":9350,"journal":{"name":"British Journal of Applied Physics","volume":"206 1","pages":"1115-1120"},"PeriodicalIF":0.0,"publicationDate":"1967-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89322396","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1967-08-01DOI: 10.1088/0508-3443/18/8/316
S. W. Allison, I. Ward
The cold-drawing behaviour of polyethylene terephthalate has been studied over a wide range of test conditions and polymer constitution. In addition to measurements at different temperatures and strain rates, the influence of pre-orientation, crystallinity and chemical cross-linking was investigated. Although crystallinity and cross-linking altered to some extent the details of the drawing process, the overall pattern of behaviour remained substantially unchanged despite rather severe changes in the microstructure of the polymer. Pre-orientation affected the yield stress and produced marked changes in the natural draw ratio. Previous studies by Pinnock and Ward have shown that pre-orientation is introduced during extrusion in a manner similar to stretching a rubber network and that the degree of stretch can be determined by the subsequent high-temperature shrinkage of the pre-oriented fibre. Measurements of the natural draw ratio and shrinkage of a series of pre-oriented fibres, described here, showed that the natural draw ratio may be regarded as equivalent to stretching a network to a limiting total extension. This limiting extension appeared to be a constant independent of the division of extension between the extrusion and drawing processes, and could provide a geometrical explanation for the large influence of pre-orientation on the natural draw ratio. An alternative view is that the degree of strain hardening achieved for a given elongation during the cold-drawing process will be affected by pre-orientation, and that the natural draw ratio could be very sensitive in this respect. Even with this explanation, the change in strain hardening may be associated with the limiting extension of a network. Measurement of the birefringences and moduli of the cold-drawn fibres showed that the development of optical and mechanical anisotropy could be fitted to a good approxi mation by an aggregate theory. This theory assumes that the drawn fibre consists of an aggregate of optically and mechanically anisotropic units which are aligned by the drawing process.
{"title":"The cold drawing of polyethylene terephthalate","authors":"S. W. Allison, I. Ward","doi":"10.1088/0508-3443/18/8/316","DOIUrl":"https://doi.org/10.1088/0508-3443/18/8/316","url":null,"abstract":"The cold-drawing behaviour of polyethylene terephthalate has been studied over a wide range of test conditions and polymer constitution. In addition to measurements at different temperatures and strain rates, the influence of pre-orientation, crystallinity and chemical cross-linking was investigated. Although crystallinity and cross-linking altered to some extent the details of the drawing process, the overall pattern of behaviour remained substantially unchanged despite rather severe changes in the microstructure of the polymer. Pre-orientation affected the yield stress and produced marked changes in the natural draw ratio. Previous studies by Pinnock and Ward have shown that pre-orientation is introduced during extrusion in a manner similar to stretching a rubber network and that the degree of stretch can be determined by the subsequent high-temperature shrinkage of the pre-oriented fibre. Measurements of the natural draw ratio and shrinkage of a series of pre-oriented fibres, described here, showed that the natural draw ratio may be regarded as equivalent to stretching a network to a limiting total extension. This limiting extension appeared to be a constant independent of the division of extension between the extrusion and drawing processes, and could provide a geometrical explanation for the large influence of pre-orientation on the natural draw ratio. An alternative view is that the degree of strain hardening achieved for a given elongation during the cold-drawing process will be affected by pre-orientation, and that the natural draw ratio could be very sensitive in this respect. Even with this explanation, the change in strain hardening may be associated with the limiting extension of a network. Measurement of the birefringences and moduli of the cold-drawn fibres showed that the development of optical and mechanical anisotropy could be fitted to a good approxi mation by an aggregate theory. This theory assumes that the drawn fibre consists of an aggregate of optically and mechanically anisotropic units which are aligned by the drawing process.","PeriodicalId":9350,"journal":{"name":"British Journal of Applied Physics","volume":"616 1","pages":"1151-1164"},"PeriodicalIF":0.0,"publicationDate":"1967-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77494977","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1967-08-01DOI: 10.1088/0508-3443/18/8/319
A. Maude
The measured viscosity of a suspension appears to depend upon the diameter of the tube of the capillary viscometer used in determining it. It is shown that existing theory can be brought into satisfactory agreement with experimental results if it is assumed that the interaction between the suspended particles makes the concentration uniform across the tube. The effect of the curvature of the velocity profile on particle velocity is also included.
{"title":"Theory of the wall effect in the viscosity of suspensions","authors":"A. Maude","doi":"10.1088/0508-3443/18/8/319","DOIUrl":"https://doi.org/10.1088/0508-3443/18/8/319","url":null,"abstract":"The measured viscosity of a suspension appears to depend upon the diameter of the tube of the capillary viscometer used in determining it. It is shown that existing theory can be brought into satisfactory agreement with experimental results if it is assumed that the interaction between the suspended particles makes the concentration uniform across the tube. The effect of the curvature of the velocity profile on particle velocity is also included.","PeriodicalId":9350,"journal":{"name":"British Journal of Applied Physics","volume":"17 1","pages":"1193-1197"},"PeriodicalIF":0.0,"publicationDate":"1967-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83796124","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1967-08-01DOI: 10.1088/0508-3443/18/8/303
R. Collier, T. Wilmshurst
Theory is developed for the mid-band saturation characteristics of the ammonia maser amplifier and also for the variation of maser bandwidth with gain. Experimental results are presented for both saturation and gain-bandwidth measurements and these are compared with calculated values. For a gain of 20 dB the output saturation power is typically 10-12 W, whilst the bandwidth is in the region of 200 Hz.
{"title":"Some characteristics of the ammonia maser amplifier","authors":"R. Collier, T. Wilmshurst","doi":"10.1088/0508-3443/18/8/303","DOIUrl":"https://doi.org/10.1088/0508-3443/18/8/303","url":null,"abstract":"Theory is developed for the mid-band saturation characteristics of the ammonia maser amplifier and also for the variation of maser bandwidth with gain. Experimental results are presented for both saturation and gain-bandwidth measurements and these are compared with calculated values. For a gain of 20 dB the output saturation power is typically 10-12 W, whilst the bandwidth is in the region of 200 Hz.","PeriodicalId":9350,"journal":{"name":"British Journal of Applied Physics","volume":"177 1","pages":"1053-1059"},"PeriodicalIF":0.0,"publicationDate":"1967-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77266015","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1967-08-01DOI: 10.1088/0508-3443/18/8/306
F. C. Dockworth, J. Burke
The effects of small concentrations of silver, copper, magnesium and indium on the annealing of quenched-in vacancies in zone-refined aluminium have been studied by using electrical-resistivity measurements. All the solutes were found to retard annealing and the presence of indium introduced an additional stage in the recovery process. It is concluded that the binding energy between a vacancy and a solute atom increases in the order silver, copper, magnesium, indium.
{"title":"The annealing of quenched-in vacancies in dilute aluminium alloys","authors":"F. C. Dockworth, J. Burke","doi":"10.1088/0508-3443/18/8/306","DOIUrl":"https://doi.org/10.1088/0508-3443/18/8/306","url":null,"abstract":"The effects of small concentrations of silver, copper, magnesium and indium on the annealing of quenched-in vacancies in zone-refined aluminium have been studied by using electrical-resistivity measurements. All the solutes were found to retard annealing and the presence of indium introduced an additional stage in the recovery process. It is concluded that the binding energy between a vacancy and a solute atom increases in the order silver, copper, magnesium, indium.","PeriodicalId":9350,"journal":{"name":"British Journal of Applied Physics","volume":"436 1","pages":"1071-1077"},"PeriodicalIF":0.0,"publicationDate":"1967-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74385150","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1967-08-01DOI: 10.1088/0508-3443/18/8/422
M. Idnurm, K. Landecker
The effects of thermal-neutron irradiation on the parameters involved in the thermoelectric figures of merit of Bi2Te3 and its thermoelectric alloys have been examined. It was found that integrated fluxes of up to 2 × 1018 neutrons/cm2 are not sufficiently high to affect the figures of merit of these materials by the introduction of radiation-induced phonon scattering centres. On the other hand, the results indicated that if still higher fluxes were employed it would become necessary to resort to excessive counter-doping in order to maintain the carrier densities in the materials at the optimum values.
{"title":"RESEARCH NOTES: Changes produced in thermoelectric materials by thermal-neutron irradiation","authors":"M. Idnurm, K. Landecker","doi":"10.1088/0508-3443/18/8/422","DOIUrl":"https://doi.org/10.1088/0508-3443/18/8/422","url":null,"abstract":"The effects of thermal-neutron irradiation on the parameters involved in the thermoelectric figures of merit of Bi2Te3 and its thermoelectric alloys have been examined. It was found that integrated fluxes of up to 2 × 1018 neutrons/cm2 are not sufficiently high to affect the figures of merit of these materials by the introduction of radiation-induced phonon scattering centres. On the other hand, the results indicated that if still higher fluxes were employed it would become necessary to resort to excessive counter-doping in order to maintain the carrier densities in the materials at the optimum values.","PeriodicalId":9350,"journal":{"name":"British Journal of Applied Physics","volume":"48 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"1967-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86050239","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1967-08-01DOI: 10.1088/0508-3443/18/8/127
I. Saunders
If the recombination lifetime is a rapid function of temperature, thermally stimulated luminescence and conductivity are not related by a constant scale factor. It is thus not permissible to assume that the published theory describes both cases. This is discussed with particular reference to the theory of Garlick and Gibson.
{"title":"The relationship between thermally stimulated luminescence and thermally stimulated conductivity","authors":"I. Saunders","doi":"10.1088/0508-3443/18/8/127","DOIUrl":"https://doi.org/10.1088/0508-3443/18/8/127","url":null,"abstract":"If the recombination lifetime is a rapid function of temperature, thermally stimulated luminescence and conductivity are not related by a constant scale factor. It is thus not permissible to assume that the published theory describes both cases. This is discussed with particular reference to the theory of Garlick and Gibson.","PeriodicalId":9350,"journal":{"name":"British Journal of Applied Physics","volume":"62 1","pages":"1219-1220"},"PeriodicalIF":0.0,"publicationDate":"1967-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90615981","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1967-08-01DOI: 10.1088/0508-3443/18/8/313
M. Sodha, S. Sharma
The coefficient of recombination of electrons with negatively charged solid particles and the rate of thermionic emission from such particles are calculated by using an appropriate expression for the potential energy of electrons near the surface of the particles instead of the idealized relationship used in an earlier paper by M. S. Sodha. The results are discussed together with relevant numerical data.
{"title":"ELECTRON RECOMBINATION AND THERMIONIC EMISSION IN NEGATIVELY CHARGED SOLID PARTICLES.","authors":"M. Sodha, S. Sharma","doi":"10.1088/0508-3443/18/8/313","DOIUrl":"https://doi.org/10.1088/0508-3443/18/8/313","url":null,"abstract":"The coefficient of recombination of electrons with negatively charged solid particles and the rate of thermionic emission from such particles are calculated by using an appropriate expression for the potential energy of electrons near the surface of the particles instead of the idealized relationship used in an earlier paper by M. S. Sodha. The results are discussed together with relevant numerical data.","PeriodicalId":9350,"journal":{"name":"British Journal of Applied Physics","volume":"104 1","pages":"1127-1131"},"PeriodicalIF":0.0,"publicationDate":"1967-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79593978","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1967-08-01DOI: 10.1088/0508-3443/18/8/305
D. Ballentyne, D. Lacklison
The thermomagnetic figures of merit of bismuth for different crystallographic orientations have been measured at 77°K for magnetic fields up to 12 kOe. The magnetoresistance ratios were also determined for fields of 10 kOe. The experimental results for the high-field figure of merit are consistent with theoretical calculations based on Abeles and Meiboom's model for the band structure of bismuth.
{"title":"Thermomagnetic figures of merit of bismuth at 77°K","authors":"D. Ballentyne, D. Lacklison","doi":"10.1088/0508-3443/18/8/305","DOIUrl":"https://doi.org/10.1088/0508-3443/18/8/305","url":null,"abstract":"The thermomagnetic figures of merit of bismuth for different crystallographic orientations have been measured at 77°K for magnetic fields up to 12 kOe. The magnetoresistance ratios were also determined for fields of 10 kOe. The experimental results for the high-field figure of merit are consistent with theoretical calculations based on Abeles and Meiboom's model for the band structure of bismuth.","PeriodicalId":9350,"journal":{"name":"British Journal of Applied Physics","volume":"9 6 1","pages":"1065-1069"},"PeriodicalIF":0.0,"publicationDate":"1967-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82698115","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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